The present process is an improvement of an earlier process wherein a nitrogen enriched gas is obtained from a gas containing at least oxygen and possibly other components in addition to nitrogen, such as, for instance, air. In the earlier process a carbonaceous molecular sieve coke in an adsorber is evacuated and then charged with nitrogen containing gas in a continuous flow cycle. Principally oxygen is adsorbed by the sieve coke and the discharged nitrogen-rich product gas is collected until its continually rising oxygen contents has reached a predetermined limit value. The charged molecular sieve coke is then desorbed of the residual gases whereupon it can be again charged with nitrogen-rich gases. The evacuation of the molecular sieve coke in this process was normally effected up to a pressure below 120 torr and preferably between 70 and 20 torr and the charging of the adsorber and flow of nitrogen containing gases therethrough was carried out at a constant pressure between 1 and 5 bar.
There was thus obtained a concentration increase of nitrogen in the product gas up to 93 to 99.5%. This result applies to a single step process in two alternatingly charged adsorbers. Only if the process is carried out in two stages with four adsorbers and the nitrogen enriched product gas of the first stage is then again subjected to the same process step is it possible to obtain a concentration of nitrogen in the product gas up to 99.9%. However, the two-stage process is very expensive.
It is therefore an object of the present invention to provide for an improvement of the concentration of nitrogen in the product gas so as to obtain a concentration of 99.9% even with a single-stage process.